1. Technical Field
The present invention relates to wireless communication and, more particularly, to a method and apparatus of downlink subchannelization in a wireless communication system.
2. Related Art
IEEE (Institute of Electrical and Electronics Engineers) 802.16e standards have been adapted in the name of ‘WMAN-OFDMA TDD’ as sixth standards for IMT (International Mobile Telecommunication)-2000 in ITU (International Telecommunication Union-affiliated ITU-R (ITU-Radio communication sector) in 2007. ITU-R is preparing an IMT-Advanced system as next-generation 4G mobile communication standards after IMT-2000. IEEE 802.16 WG (Working Group) has determined to promote an 802.16m project to aim at creating amendment standards of the existing IEEE 802.16e, as standards for the IMT-Advanced system in late 2006. As noted from the aim, 802.16m standards involve the continuity of the past 802.16e standards and the continuity of the futuristic next-generation IMT-Advanced system. Thus, 802.16m standards are required to satisfy the advanced requirements for the IMT-Advanced system while maintaining the compatibility with the 802.16e standard-based Mobile WiMAX system.
One of the systems considered in the next wireless communication generation is an OFDM (Orthogonal Frequency Division Multiplexing) system that can attenuate an inter-symbol interference (ISI) effect with low complexity. The OFDM converts serially input data symbols into N number of parallel data symbols, includes them in the N number of separated subcarriers, and transmits the same. The subcarriers maintain orthogonality in a frequency domain. Respective orthogonal channels experience mutually independent frequency selective fading, and the intervals of transmitted symbols are lengthened to thus minimize the inter-symbol interference. OFDMA (Orthogonal Frequency Division Multiple Access) refers to a multi-access scheme accomplishing multiple accesses by independently providing portions of available subcarriers to each user in a system using the OFDM as a modulation scheme. The OFDMA provides frequency resources called subcarriers to each user, and in general, the respective frequency resources are independently provided to multiple users so as not to overlap with each other. That is, resultantly, frequency resources are mutually exclusively allocated to the users.
In the OFDMA system, frequency diversity can be obtained for multiple users through frequency selective scheduling, and subcarriers can be allocated in various forms according to permutation with respect to the subcarriers. The efficiency of a space domain can be enhanced according to a space multiplexing scheme using multiple antennas.
Meanwhile, radio resources may be divided into a plurality of frequency partitions (FP) when a service such as a multicast and broadcast service is provided. This is called a fractional frequency reuse (FFR), and each of the frequency partitions can be used for each different purposes. In each of the frequency partitions, distributed subchannels and localized subchannels may coexist according to a frequency division multiplexing scheme. Also, subchannels may be allocated to the respective frequency partitions based on different resources units (or granularity).
A base station (BS) may use an open loop (OL) region. The OL region is a time frequency resource domain using the same number of pilot patterns and a given OL multi-input multi-output (MIMO) mode. The OL region is used to provide a stable interference environment. However, the OL region is classified into several types of regions according to the type of supported permutations, applied MIMO feedback modes, and the like. In order for the BS to use the OL region, resource units of each cell must be aligned. In this case, however, the existing subchannelization method has a problem in that some types of the OL region are not able to align corresponding resource units.
Thus, a method and an apparatus of downlink subchannelization for supporting any type of OL region is required.